Functional films composed of ferroelectric material or piezoelectric material are used in some electronic devices such as film capacitors, ferroelectric nonvolatile memories, film bulk acoustic wave resonators and the like. A film bulk acoustic wave resonator, for instance, is configured by sandwiching a functional film made of a piezoelectric material between an upper conductive film and a lower conductive film. The film bulk acoustic wave resonator operates as a high-frequency filter when a high-frequency signal is applied across the two conductors.
To achieve good device characteristics in such an electronic device, it is necessary to enhance the crystallinity of the functional film. A method of improving the crystallinity of the lower conductive film that is generally employed is to improve the crystallinity of the lower conductive film and have that crystallinity reflected in the crystallinity of the functional film. For example, U.S. Pat. No. 6,475,931 and Japanese Patent Application Laid Open No. 2001-313535 teach a method in which the X-ray rocking curve full width at half maximum (FWHM) of the lower conductive film is made to be not greater than 4.5 degrees, and by reflecting that crystallinity, a functional film X-ray rocking curve FWHM of not more than 3.5 degrees is achieved. JP 3,310,881 and Japanese Patent Application Laid Open No. 11-312801 also describe methods of forming a lower conductive film having good crystallinity.
However, in order to have the crystallinity of the lower conductive film adequately reflected in the functional film, it is necessary to use a costly method of growing the film, such as, for example, epitaxial growth. Moreover, with an epitaxial growth method, the film growth rate is relatively low, so low productivity is a problem when the method is used to form functional films.
Furthermore, to have the crystallinity of the lower conductive film reflected in the crystallinity of the functional film, it is also necessary to form the lower conductive film of expensive materials having high crystal matching to the functional film, such as, for example, platinum (Pt) and iridium (Ir), so the high cost of the materials becomes a problem. The crystallinity of the lower conductive film is also not reflected in the functional film if the lower conductive film has a high surface roughness, so in some cases it is necessary to smooth the surface of the lower conductive film by polishing or the like.